1. Field of the Invention
The present invention relates to a reflective liquid crystal display device.
2. Description of the Related Art
In a reflective liquid crystal display device, the brightness of a screen is obtained by reflecting external light such as sunlight or indoor light. However, in the case where only reflected external light is used, when the screen cannot be made sufficiently bright at a place where there is not much external light, the amount of reflected external light is supplemented by disposing a flat light source device (hereinafter referred to as xe2x80x9cfront lightxe2x80x9d) using a transparent plate at a display surface side of a liquid crystal display panel.
FIG. 17 schematically illustrates the structure of a conventional reflective liquid crystal display device using a front light. A structure similar to this is disclosed in, for example, Japanese Unexamined Patent Application Publication No. Hei. 8-94844(1996). In FIG. 17, reference numeral 1 denotes a reflective liquid crystal display panel, and reference numeral 1a denotes a display surface which is the surface that an observer looks at in order to look at an image produced on the liquid crystal display panel 1. Reference numeral 2 denotes a light-guiding plate disposed on the side of the display surface 1a of the liquid crystal display panel 1. A prism array 2b is formed at a side opposite to the side of a bottom surface 2a opposing the display surface 1a of the liquid crystal display panel 1. In the prism array 2b, crest lines T and trough lines V, which extend in a perpendicular direction with respect to the plane of the figure and which are parallel to each other, are alternately provided. As shown in FIG. 17, a tilt angle xcex1 of a tilted surface S1 of the prism array 2b is, for example, approximately 45 degrees, while a tilt angle xcex2 of a tilted surface S2 is, for example, equal to or less than 10 degrees.
Reference numeral 3 denotes a light source disposed beside a light-incident surface 2c of the light-guiding plate 2, and reference numeral 4 denotes a reflector for reflecting light generated from the light source 3 to efficiently cause the light to be incident upon the light-guiding plate 2 from the light-incident surface 2c. Reference numeral 5 denotes a reflecting plate disposed so that the light from the light source 3 does not exit from surfaces of the light-guiding plate 2 other than the bottom surface 2a and the surface of a prism array 2b. The front light is formed by the light-guiding plate 2, the light source 3, the reflector 4, and the reflecting plate 5.
A description of an optical path from where light is generated from the light source 3 to where it exits from the display surface of the liquid crystal display device will now be given.
The light generated from the light source 3 is directly reflected or reflected by the reflector 4, and impinges upon the light-guiding plate 2 from the light-incident surface 2c. The light incident upon the light-incident surface 2c while repeatedly being subjected to total reflection due to the difference between the refractive indices of the light-guiding plate 2 and air is transmitted through the inside of the light-guiding plate 2 towards the opposite side of the lamp 3. When the light strikes the tilted surface S1 of the prism array 2b, it is reflected in a direction substantially perpendicular to the bottom surface 2a, so that the condition for total reflection of light inside the light-guiding plate 2 is broken, causing the light to exit from the bottom surface 2a. The light which has exited from the bottom surface 2a is incident upon the liquid crystal display panel 1, is modulated by a liquid crystal layer (not shown) of the liquid crystal display panel, and is reflected by a reflecting surface (not shown) of the liquid crystal display panel. Thereafter, the light passes through the light-guiding plate 2 again, and exits therefrom in the direction of the observer at the display surface side. Reflected light is produced at the bottom surface 2a of the light-guiding plate 2 or the display surface 1a of the liquid crystal display panel 1.
In the conventional reflective liquid crystal display device, external light and light from the light source 3 are not only reflected at the reflecting surface of the reflective liquid crystal display panel 1, but also reflected at the bottom surface 2a of the light-guiding plate 2 and the display surface 1a of the liquid crystal display panel 1. Therefore, the light becomes undesired reflected light not carrying image information (hereinafter referred to as xe2x80x9cundesired lightxe2x80x9d) as a result of not passing through the liquid crystal layer of the liquid crystal display panel 1, thereby resulting in the problem that contrast is reduced.
A method of overcoming the above-described problem is disclosed in, for example, Japanese Unexamined Patent Application Publication No. Hei. 11-242220(1999). In this document, the method provides a reflection preventing film at the bottom surface 2a of the light-guiding plate. The document proposes to overcome the problem of reduced contrast of the displayed image caused by the reflection at the bottom surface 2a when light exits from the light-guiding plate 2 by providing the reflection preventing film. However, even when the reflection preventing film is provided, the reflection of undesired light of the order of 0.5% occurs, thereby resulting in the problem that sufficient contrast cannot be obtained.
Accordingly, the present invention has been achieved to overcome the above-described problem, and has as its object the provision of a reflective liquid crystal display device which can provide high contrast even when there is undesired light.
To this end, according to one aspect of the present invention, there is provided a reflective liquid crystal display device including a light source; a light-guiding plate, in which light from the light source is received from a side surface of the light-guiding plate, and in which the light exits from a bottom surface of the light-guiding plate; and a reflective liquid crystal display panel disposed so as to be parallel to and so as to oppose the bottom surface of the light-guiding plate, the reflective liquid crystal display panel having a liquid crystal layer sandwiched between an upper substrate and a lower substrate. In the reflective liquid crystal display device, a deflecting device for deflecting the light which has exited from the bottom surface of the light-guiding plate is provided at a top surface side of the upper substrate of the reflective liquid crystal display panel. Thus, the light from the light source exiting from the bottom surface of the light-guiding plate can be reflected by the deflecting device in a direction that is tilted from the vertical direction, which is the visual recognition direction. Therefore, it is possible to provide high contrast.
According to another aspect of the present invention, there is provided a reflective liquid crystal display device including a reflective liquid crystal display panel having a liquid crystal layer sandwiched between an upper substrate and a lower substrate. In the reflective liquid crystal display device, a deflecting device for deflecting light incident from a top surface side of the upper substrate is provided at the top surface side of the upper substrate of the reflective liquid crystal display panel. Thus, external light can be reflected at the deflecting device in a direction that is tilted from the vertical direction, which is the visual recognition direction. Therefore, it is possible to provide high contrast.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.